1. Field of the Invention
The present invention relates generally to a multifunctional visceral catheter which is substantially self-guiding, i.e., which may be positioned in a visceral venous system without the need for bedside fluoroscopy or other x-ray devices.
More particularly, the self-guiding system of the catheter according to the invention comprises a fiberoptic sensor system, such as a biochemical substrate optode system, which is sensitive to a predetermined analyte or metabolite. The predetermined analyte has a specific relationship to the organ associated with a given visceral venous system such that values of the analyte within the visceral venous system are substantially different from systemic values of the analyte outside the visceral venous system. In particular, the predetermined analyte may be one having a substantial extraction fraction across the splanchnic bed or vascular circuit being explored. When the catheter according to the invention is properly positioned in the hepatic or renal vein, for example, signals received from the sensor(s) of the fiberoptic system will reflect a sudden, substantial decrease in the given analyte so as to readily confirm proper positioning of the catheter.
The catheter according to the invention is also capable of performing various monitoring and assessment functions. The catheter is capable of continuously monitoring the oxygen saturation in the hepatic or renal venous blood once the catheter is placed in any major hepatic or renal venous vessel. The catheter according to the invention is further capable of measuring absolute hepatic or renal blood flow using a tracer clearance technique. The catheter also permits direct sampling of venous blood, such as hepatic or renal venous blood, for the ex vivo measurement of metabolite concentrations.
2. Description of Relevant Art
Known methods of diagnosing liver and/or kidney dysfunction, as well as assessing various physiological parameters associated with the functioning of these organs, typically require catheterization of the hepatic or renal venous systems. A principal disadvantage associated with known techniques for catheterizing the hepatic and renal venous systems is that bedside fluoroscopy or other x-ray devices are required in order to properly position the catheter. For example, while a thermodilution catheter has been developed for renal blood flow determination which might be applicable to general clinical use, the need for fluoroscopic assistance in positioning such catheter is a critical shortcoming. See M. Brenner, G. L. Schaer, D. L. Mallory, et al, "Detection of renal blood flow abnormalities in septic and critically ill patients using a newly designed indwelling thermodilution renal vein catheter", Chest, Vol. 98, pp. 170-79 (1990).
The present inventors, in their invention disclosed and described in their aforesaid U.S. patent application Ser. No. 332,715 filed Nov. 1, 1994, have overcome the principal shortcoming of known catheterization techniques by providing a self-guiding visceral catheter which can be positioned in either the hepatic or the renal venous systems without the use of bedside fluoroscopy or other x-ray devices. The catheter body preferably comprises a main axial portion with an angled end portion extending therefrom at an acute angle. A sensor disposed on the main axial portion of the catheter is adapted to remain outside the visceral venous system, while a sensor disposed on the angled end portion of the catheter is adapted to be positioned within the visceral venous system. Each of the sensors comprises an electrochemical sensing system including an electrode with a hydratable membrane containing a reagent which detects values of a predetermined analyte. The predetermined analyte is related to the organ associated with the given visceral venous system such that values of the analyte within the visceral venous system are substantially different from systemic values of the analyte outside the visceral venous system. Proper positioning of the catheter within the visceral venous system is readily and immediately confirmed by a large difference in analyte concentrations detected by the two electrochemical sensor systems. Alternatively, a single sensor may be provided on only the angled end portion of the catheter, with proper positioning being confirmed by a substantial decrease in analyte concentration as detected by the single electrochemical sensor system.
Like the visceral catheter of the invention disclosed in U.S. patent application Ser. No. 332,715, the visceral catheter according to the present invention incorporates a self-guiding system which is responsive to the differences in values of a predetermined analyte as measured within the visceral venous system of interest as opposed to outside the visceral venous system so as to confirm correct positioning of the catheter. However, in the visceral catheter according to the present invention, the electrochemical sensor systems are replaced by fiberoptic biochemical sensor systems of various suitable types. Some of the advantages afforded by the use of fiberoptic biochemical sensors include eliminating any direct electrical connection to the patient; avoiding potential electrical interference problems; enhanced detection capabilities; and reduction in size and/or expense of various components.
The visceral catheter according to the invention is multifunctional inasmuch as it also permits continuous monitoring of the oxygen saturation in the hepatic or renal venous blood. In the absence of any known technique for readily assessing individual organ oxygenation, central mixed venous oxygen saturation has commonly been used as an index of global body oxygenation. However, the results of various studies have shown that a marked reduction in hepatic venous oxygen saturation frequently exists in critically ill patients. See, e.g., Michael S. Dahn, M. Patricia Lange, Robert F. Wilson, Lloyd A. Jacobs, and Robert A. Mitchell, "Hepatic blood flow and splanchnic oxygen consumption measurements in clinical sepsis," Surgery, Vol. 107, No. 3, pp. 295-301 (March, 1990). This condition goes undetected when only global body oxygenation is assessed, leaving the physician unaware of a condition which could be therapeutically addressed through the use of cardioactive drugs or blood transfusion. To overcome this problem, the multifunctional visceral catheter according to the present invention is capable of continuously monitoring regional oxygenation. Once the catheter is placed in a major hepatic vessel, hepatic function can be assessed in a more direct fashion than is possible by conventional means, such as by monitoring serum bilirubin or liver enzymes.
The multifunctional catheter according to the invention also permits convenient, direct monitoring of the renal venous system. By positioning the catheter according to the invention in the renal vein, endogenous creatinine clearance and other renal functional indicators can be critically assessed. Further, if inulin and/or para-aminohypurate are available for intravenous infusion, glomerular filtration rate and renal blood flow can be assessed.